The invention relates to a process and an apparatus for adding additives during the conditioning of animal feed.
Animals receive their feed predominantly either in pulverulent form (meal) or as pressed pellets. In addition to the main feed components, animal feed generally also comprises additives, such as enzymes, vitamins or antibiotics. Such additives can be added to the feed in different ways.
U.S. Pat. No. 6,056,822 describes a general process for any desired types of animal feed, in which feed additives, for example enzymes, are applied in dissolved form to cooled feed pellets in what is termed the xe2x80x9cPPA (Post Pelleting Application) processxe2x80x9d, that is to say after the pelletizing process. The advantage of this method is that the substances applied do not suffer any loss in activity due to the action of heat owing to the conditioning step which precedes the feed pelletizing. A disadvantage is that the additives cannot be applied to the pellets in powder form and, in addition, technically complex equipment is required in order to enable the metering, dissolution and spraying of enzyme solutions. In addition to the extensive equipment requirements and the associated costs, there is a further disadvantage of the PPA process, namely the fact that the additives to be applied are not always distributed homogeneously on the feed.
DE-A 43 06 514 describes a process and an apparatus in which, within the pelletizing machine, lignin sulfone-based pressing aids are added to the feed to be pressed. However, using this method only those liquids can be sprayed or atomized onto the material to be pressed that do not prevent processing of the material to be pressed in the press owing to excessive moisture content. A further disadvantage of this method is that homogeneous mixing of the added liquid with the material to be pressed is not ensured in this manner.
WO 99/51107 indicates a process for producing fish food in which dissolved enzymes are added to the main food constituents as early as before the conditioning step. The enzyme used in this case, transglutaminase, acts to catalyze a reaction of proteins present in the food and also stabilizes the shape of the pellets produced. The advantage of this method is that the enzymes are mixed better with the food, which results in a homogeneous distribution of all additives. However, the food mixture, including the added enzymes, undergoes very great stress during the conditioning step, and during the subsequent pelletizing step. This stress is all the greater, the higher the temperatures employed and the residence time of the food in the conditioning unit and the pelletizing unit. This means that the enzyme activity of the end product is very greatly, or at least considerably, limited. For this reason, the food mixture can be exposed to a maximum of 60xc2x0 C., and the additives are admixed in a very great excess, compared with the PPA process.
WO 98/54980 describes a process in which dissolved enzymes are formed with a stabilizer to give granules which then pass, together with the main feed components, through a conditioning and pelletizing process. Because of the action of the granule carrier material, which consists of carbohydrates, the admixed enzymes exhibit increased stability, nevertheless they must be used in a great excess, in order to be able to make up for the loss of activity during the conditioning and pelletizing process. A further disadvantage of this process is also that the production of the enzyme-containing granules is associated from the beginning with additional costs and is time-consuming.
It is an object of the present invention to develop a process in which, firstly, additives are added to the feed in a smaller amount and inexpensively, that is to say using less equipment, and secondly these additives are uniformly distributed in the pelletized feed end product.
We have found that this object is achieved by a process and an apparatus underlying the process which comprise the following features:
a) the feed is transferred from a container via a feed screw at an inlet point into a conditioner,
b) the feed is transported in the conditioner by a mixing screw from the inlet point along a path to an exit point, and is exposed to vapor in the course of this,
c) one or more additives which are introduced into the conditioner through one or more ports are added to the feed which has passed through x% of the path in the conditioner,
d) the feed and the additives added through one or more ports are mixed on the remaining (100-x)% of the path to form a mixture,
e) the mixture leaving the conditioner at the exit point is transferred to a pelleting press,
f) the mixture is formed into pellets in the pelleting press
g) and the pellets are finally transferred to a cooling device.
The great advantage of this process is that the additives, in particular enzymes, vitamins, carotenoids and antibiotics are not added to the main feed components until toward the end of the conditioning step. In this manner, these relatively heat-labile substances are only exposed to elevated temperatures for a relatively short time and experience much less stress than would be the case with complete passage through the conditioning unit. This considerably reduces the loss in activity of the substances added. As a result, significantly smaller amounts of these in part very expensive substances are required, considerably reducing the production costs of pelleted animal feed that comprises additives.
In addition, as a result of the significantly reduced residence time of the additives in the conditioning unit, the temperatures of in each case approximately 80xc2x0 C. (and above) which are customary in the conditioning and pelletizing steps can be employed, as a result of which more stable pellets are produced. A further advantage of the inventive process is the fact that the additives are still sufficiently well mixed with the main feed components to achieve homogeneous distribution in the feed pellets.
A further advantage is that the inventive process is suitable in particular for adding solids, as a result of which the dissolution and exact metering of the solution of these additives, which are not only time-consuming but also require complex equipment, are avoided as are problems of adhesion to the pellets.